Heretofore, various methods of forming a ceramic porous membrane on a porous base member have been known. For example, a hot coating process is known (see Non-Patent Document 1). This is a method of rubbing a tube base member with cloth containing a silica sol to apply the silica sol and thereby form a porous membrane on an outer surface of the heated tube base member.
A method of forming a porous membrane on an inner surface of a porous base member having a tubular shape or a cylindrical lotus-root-like monolith shape by filtering membrane formation is also known (see Patent Document 1). The outer surface of the porous base member is held at a pressure lower than that of an inner surface thereof which comes in contact with a sol liquid to form the membrane on the inner surface of the porous base member.
Patent Document 1: Japanese Patent Application Laid-Open No. 3-267129
Patent Document 2: Japanese Patent Application Laid-Open No. 61-238315
Non-Patent Document 1: Tsuru et al., “Silica-Zirconia Membranes for Nanofiltration,” Journal of Membrane Science, 149 (1988), pp. 127 to 135
However, the hot coating process has a problem that the membrane cannot uniformly be formed on the whole base surface, and the membrane can be formed on the only outer surface of the tube base member. The process cannot be applied to any monolith-type base. On the other hand, in the filtering membrane formation process, during drying of the formed membrane, a solvent present in base pores sometimes flows out on a membrane side to cause membrane peeling. As a result, there is a problem that a defect is generated in the porous membrane formed on the fired base surface. A dip coating process can be applied to the monolith type base, but the number of membrane formation times is large.